This invention relates to a variable length frame exchanging method, a variable length frame exchanging interface apparatus and a call acceptance determination system adapted for a fixed length cell handing exchange in which a terminal for use with a data communication system by a variable length frame is accommodated.
In recent years, as the introduction of the ISDN (Integrated Services Digital Network) proceeds, the utilization of public networks is complicated such that a public network, which has offered only telephone services, can now offer such various communication services as data communications, facsimile communications and packet communications at home of each of subscribers. Further, as the amount of communications increases, not only speech but also video signals and so forth can be transmitted. In this manner, various information communications are available nowadays. Particularly it is advantageous in terms of the cost and/or the communication speed to communicate data by way of an ISDN.
Meanwhile, the CCITT recommends a data communication method by a variable length frame including logic channel information, for example, a frame relay, for data communications. The frame relay is adapted to a common packet exchanging system and is expected as a technique which meets the requirement for a high speed packet service. In the frame relay technique, no protocol for a layer higher than the layer 2 is defined and the network does not participate in the protocol since frame multiplexing is performed in the data link layer, and accordingly, hardware matching is easy comparing with a packet exchanging system based on the X25 which is a protocol for the layer 2 and an increase in throughput can be realized.
Further, in popular packet exchanging systems, repeat control based on a protocol of a LAP-B is performed between a terminal and a network (exchange) or between different exchanges. With a frame relay, however, repeat control is not performed between a terminal and a network, and consequently, high speed transmission can be achieved together with an additional reason that no controlling processing for the repeat control is required.
By the way, in recent years, an ATM (Asynchronous Transfer Mode) exchange technique has been consented as a next generation exchange system by the CCITT, and investigations have been and are being directed actively toward the ATM exchange technique as a technique which realizes a broad band ISDN (B-ISDN). With an ATM exchange (fixed length cell handling exchange), user information is exchanged in the form of a packet of a fixed length called cell which includes united contents (data, sound, images and so forth) of information. As development of such ATM exchange technique proceeds, it is desired that also the service for accommodating and connecting a terminal (hereinafter referred to as frame relay terminal) for a frame relay described above into and to an ATM exchange network can be offered as one of services of the ATM exchange network.
An example for reference of a system wherein an ISDN frame relay is used to interconnect a plurality of LANs (Local Area Networks) is illustrated in FIG. 44. Referring to FIG. 44, a plurality of personal computers (frame relay terminals) 11 to 16 are shown, and a LAN 21 is constituted from the personal computers 11 and 12; another LAN 22 is constituted from the personal computers 13 and 14; and a further LAN 23 is constituted from the personal computers 15 and 16. The LANs 21 to 23 are connected to exchange offices 51 to 53 by way of ISDN interfaces 31 to 33 and circuit terminating equipments (NT) 41 to 43, respectively, so that they are connected to each other by way of a public network (ISDN) 60.
In such a system as described above, establishment of a transmission channel is performed using a call control protocol (I.451), but a transmission channel may otherwise be established in response to a command from a service person. Meanwhile, a LAP-F (Link Access Protocol-Frame Relay) is used for frame transmission (popular packet transmission). Data transmission is thus allowed between arbitrary terminals (personal computers 11 to 16). In particular, each of the personal computers 11 to 16 can communicate with an arbitrary one of the other personal computers 11 to 16 by performing data communication by way of a logical link (identified with a DLCI (Data Link Connection Identifier) in the signal) number of the LAP-F applied on the communication channel.
In this instance, the transmission channel between any one of the LANs 21 to 23 and a corresponding one of the exchange offices 51 to 53 can have an arbitrary line speed, and each of the LANs 21 to 23 can select a desired line speed. For example, a PCM circuit (24 channels or 30 channels) is used for the interface with each subscriber, and arbitrary channels desired by the subscribers can be combined to determine a line speed. In short, a subscriber can select a line speed from among up to 64xc3x9724 channels (or 64xc3x9730 channels) to the utmost.
However, where the network shown in FIG. 44 is a broad band ISDN which makes use of an ATM exchange, a frame relay has a subject to be solved in that, since it involves a variable frame length similarly to that of the popular packet exchange system X25, it cannot achieve high speed exchanging processing comparing with switching which employs a packet (cells) of a fixed length such as in an ATM.
Further, the CCITT does not involve provisions for the inside of a network (that is, for the inside of an exchange) when a frame relay terminal is accommodated into an ATM exchange, and the method of realizing such accommodation depends upon the maker of the system. For example, in the system shown in FIG. 44, a communication channel is connected between arbitrary ones of the subscribers (personal computers 11 to 16), and when any of the subscribers tries to transmit data to the other party, a function of routing to the other party designated by a DLCI number is required.
Meanwhile, in order to accommodate a frame relay terminal into an ATM exchange and set a path, a system has been proposed wherein acceptance of a call is determined from a peak value (a value reported from the user) of a band used between terminals between which communications are to be performed and a band for the path is allocated in accordance with the determination. Accordingly, when a user of a frame relay terminal makes a request to set a path of a band higher than a physical line speed (physical maximum speed), the path cannot be set nor connected.
However, a frame relay service allows, in most cases, the contract of generally 200 to 300% of the physical line speed, and also when a frame relay service is offered with an ATM exchange, the conditions must be the same as those in the existing service. Therefore, when a frame relay terminal is to be accommodated into an ATM exchange, it is desired to allow determination of acceptance of a call from a frame relay terminal while adopting the same conditions as those of the existing frame relay service.
It is an object of the present invention to provide a variable length frame exchanging method and a variable length frame exchanging interface apparatus by which a frame having a variable data length can be exchanged at a high speed in a fixed length cell handling exchange network.
It is another object of the present invention to provide a call acceptance determination system wherein a path for a variable length frame can be set in a fixed length cell handling exchange network in the same conditions as those in an existing service to realize a service for connecting and accommodating a variable length frame terminal to and into the fixed length cell handling exchange.
In order to attain the objects described above, according to an aspect of the present invention, there is provided a variable length frame exchanging method by a fixed length cell handling exchange which handles fixed length cells each including a logic channel information section and a data section and to which a terminal for use with a data communication method by a variable length frame including logic channel information is connected by way of a subscriber line having at least one channel, comprising the steps of disassembling, when a transmission frame is transmitted from the terminal to the exchange, the transmission frame into fixed length cells, converting a channel number or numbers of the subscriber line which has been used to transmit the transmission frame from the terminal and data link connection identifier information as the logic channel information added to the transmission frame into communication channel identifier information for the logic channel information sections of the fixed length cells, adding the communication channel identifier information to the logic channel information section of each of the fixed length cells and inputting the fixed length cells to the exchange, and exchanging the frame from the terminal as the fixed length cells in accordance with the communication channel identifier information by means of the exchange.
The communication channel identifier information may include virtual path identifier information and virtual channel identifier information, and the channel number or numbers of the subscriber line which have been used to transmit the transmission frame from the terminal may be converted into virtual path identifier information while the data link connection identifier information to be added to the transmission frame is converted into virtual channel identifier information.
According to another aspect of the present invention, there is provided a variable length frame exchanging method by a fixed length cell handling exchange which handles fixed length cells each including a logic channel information section and a data section and to which a terminal for use with a data communication method by a variable length frame including logic channel information is connected by way of a subscriber line having at least one channel, comprising the steps of producing, when fixed length cells designating the terminal as a destination of transmission are outputted from the exchange to the subscriber line, a call-in frame from the fixed length cells, converting communication channel identifier information of the logic channel information section of each of the fixed length cells into data link connection identifier information and a channel number or numbers of the subscriber line which are available to transmit the call-in frame to the terminal, and adding the data link connection identifier information as logic channel information to the call-in frame and transmitting the call-in frame to the terminal using a channel or channels of the channel number or numbers of the subscriber line obtained by conversion from the communication channel identifier information.
The communication channel identifier information may include virtual channel identifier information and virtual path identifier information, and the virtual channel identifier information may be converted into data link connection identifier information while the virtual path identifier information is converted into a channel number or numbers of the subscriber line which are available to transmit the virtual path identifier information to the terminal.
According to a further aspect of the present invention, there is provided a variable length frame exchanging method by a fixed length cell handling exchange which handles fixed length cells each including a logic channel information section and a data section and to which a terminal for use with a data communication method by a variable length frame including logic channel information is connected by way of a subscriber line having at least one channel, comprising the steps of disassembling, when a transmission frame is transmitted from the terminal to the exchange, the transmission frame into fixed length cells, converting a channel number or numbers of the subscriber line which has been used to transmit the transmission frame from the terminal and data link connection identifier information as the logic channel information added to the transmission frame into communication channel identifier information for the logic channel information sections of the fixed length cells, adding the communication channel identifier information to the logic channel information section of each of the fixed length cells and inputting the fixed length cells to the exchange, and exchanging the frame from the terminal as the fixed length cells in accordance with the communication channel identifier information by means of the exchange, but producing, when fixed length cells designating the terminal as a destination of transmission are outputted from the exchange to the subscriber line, a call-in frame from the fixed length cells, converting communication channel identifier information to be added to the logic channel information section of each of the fixed length cells into data link connection identifier information and a channel number or numbers of the subscriber line which are available to transmit the call-in frame to the terminal, and adding the data link connection identifier information as logic channel information to the call-in frame and transmitting the call-in frame to the terminal using a channel or channels of the channel number or numbers of the subscriber line obtained by conversion from the communication channel identifier information.
The variable length frame exchanging method may be constructed such that the communication channel identifier information includes virtual path identifier information and virtual channel identifier information, and a first corresponding relationship between the virtual path identifier information and a channel number or numbers of the subscriber line used between the terminal and the exchange and a second corresponding relationship between the virtual channel identifier information and a data link connection identifier to be added to a frame are registered in advance, and wherein, when a transmission frame is to be transmitted from the terminal to the exchange, a channel number or numbers of the subscriber line which have been used to transmit the transmission frame from the terminal is converted into virtual path identifier information in accordance with the first corresponding relationship and data link connection identifier information to be added to the transmission frame is converted into virtual channel identifier information in accordance with the second corresponding relationship, but when fixed length cells designating the terminal as a destination of transmission is outputted from the exchange to the subscriber line, virtual channel identifier information to be added to each of the fixed length cells is converted into data link connection identifier information in accordance with the second corresponding relationship and virtual path identifier information to be added to each of the fixed length cells is converted into a channel number or numbers of the subscriber line which are available upon transmission to the terminal in accordance with the first corresponding relationship.
According to a still further aspect of the present invention, there is provided a variable length frame exchanging interface apparatus which is interposed in a subscriber line having at least one channel for interconnecting an exchange which handles fixed length cells each including a logic channel information section and a data section and a terminal for use with a data communication method by a variable length frame including logic channel information and performs conversion processing between fixed length cells for the exchange and a variable length frame for the terminal, comprising frame production means for producing a transmission frame based on data transmitted thereto from the terminal by way of a plurality of channels of the subscriber line, channel number to virtual path identifier information conversion means for converting a channel number or numbers of the subscriber line which have been used to transmit the transmission frame from the terminal into virtual path identifier information as communication channel identifier information for the logic channel information sections of fixed length cells, data link connection identifier information to virtual channel identifier information converter for converting data link connection identifier information as logic channel information to be added to the transmission frame into virtual channel identifier information as the communication channel identifier information for the logic channel information sections of fixed length cells, and a disassembler for disassembling the transmission frame into fixed length cells to which the virtual path identifier information obtained by conversion by the channel number to virtual path identifier information converter and the virtual channel identifier information obtained by conversion by the data link connection identifier information to virtual channel identifier information conversion means are added and sending out the fixed length cells to the exchange.
The channel number to virtual path identifier information conversion means may include first storage for storing in advance a first corresponding relationship between a channel number or numbers of the subscriber line which are used between the terminal and the exchange and virtual path identifier information as communication channel identifier information, and the data link connection identifier information to virtual channel identifier information converter may include second storage for storing in advance a second corresponding relationship between a data link connection identifier to be added to a frame and virtual channel identifier information as the communication channel identifier information.
According to a yet further aspect of the present invention, there is provided a variable length frame exchanging interface apparatus which is interposed in a subscriber line having at least one channel for interconnecting an exchange which handles fixed length cells each including a logic channel information section and a data section and a terminal for use with a data communication method by a variable length frame including logic channel information and performs conversion processing between fixed length cells for the exchange and a variable length frame for the terminal, comprising an assembler for assembling a call-in frame based on fixed length cells from the exchange designating the terminal as a destination of transmission, virtual channel identifier information to data link connection identifier information converter for converting virtual channel identifier information as communication channel identifier information for the logic channel information sections of the fixed length cells into data link connection identifier information as logic channel information to be added to the call-in frame, virtual path identifier information to channel number converter for converting virtual path identifier information as the communication channel identifier information for the logic channel information sections of the fixed length cells into a channel number or numbers of the subscriber line which are available upon transmission to the terminal, and call-in frame disassembling means for transmitting the call-in frame, to which the data link connection identifier information obtained by conversion by the virtual channel identifier information to data link connection identifier information conversion means is added, by way of a channel or channels corresponding to the channel number or numbers of the subscriber line obtained by conversion by the virtual path identifier information to channel number converter to the terminal.
Preferably, the virtual path identifier information to channel number converter includes first storage means for storing in advance a first corresponding relationship between virtual path identifier information as the communication channel identifier information and a channel number or numbers of the subscriber line which are used between the terminal and the exchange and the virtual channel identifier information to data link connection identifier information converter includes second storage means for storing in advance a second corresponding relationship between virtual channel identifier information as the communication channel identifier information and a data link connection identifier to be added to a frame.
According to a yet further aspect of the present invention, there is provided a variable length frame exchanging interface apparatus which is interposed in a subscriber line having at least one channel for interconnecting an exchange which handles fixed length cells each including a logic channel information section and a data section and a terminal for use with a data communication method by a variable length frame including logic channel information and performs conversion processing between fixed length cells for the exchange and a variable length frame for the terminal, comprising a frame assembler for producing a transmission frame based on data transmitted thereto from the terminal by way of a plurality of channels of the subscriber line, channel number to virtual path identifier information converter for converting a channel number or numbers of the subscriber line which have been used to transmit the transmission frame from the terminal into virtual path identifier information as communication channel identifier information for the logic channel information sections of fixed length cells, data link connection identifier information to virtual channel identifier information converter for converting data link connection identifier information as logic channel information to be added to the transmission frame into virtual channel identifier information as the communication channel identifier information for the logic channel information sections of fixed length cells, and transmission frame disassemble for disassembling the transmission frame into fixed length cells to which the virtual path identifier information obtained by conversion by the channel number to virtual path identifier information converter and the virtual channel identifier information obtained by conversion by the data link connection identifier information to virtual channel identifier information converter are added and sending out the fixed length cells to the exchange, a frame assembler for assembling a call-in frame based on fixed length cells from the exchange designating the terminal as a destination of transmission, virtual channel identifier information to data link connection identifier information conversion means for converting virtual channel identifier information as communication channel identifier information for the logic channel information sections of the fixed length cells into data link connection identifier information as logic channel information to be added to the call-in frame, virtual path identifier information to channel number converter for converting virtual path identifier information as the communication channel identifier information for the logic channel information sections of the fixed length cells into a channel number or numbers of the subscriber line which are available upon transmission to the terminal, and call-in frame disassembler for transmitting the call-in frame, to which the data link connection identifier information obtained by conversion by the virtual channel identifier information to data link connection identifier information converter is added, by way of a channel or channels corresponding to the channel number or numbers of the subscriber line obtained by conversion by the virtual path identifier information to channel number converter to the terminal.
Preferably, the channel number to virtual path identifier information conversion means and the virtual path identifier information to channel number converter commonly include first storage means for storing in advance a first corresponding relationship between the virtual path identifier information as the communication channel identifier information and the channel number or numbers of the subscriber line which are used between the terminal and the exchange, and the data link connection identifier information to virtual channel identifier information converter and the virtual channel identifier information to data link connection identifier information converter commonly include second storage element for storing in advance a second corresponding relationship between the virtual channel identifier information as the communication channel identifier information and the data link connection identifier to be added to a frame.
According to a yet further aspect of the present invention, there is provided a call acceptance determination system for a fixed length cell handling exchange in which one or more first terminals for use with a data communication method by fixed length cells each including a logic channel information section and a data section and one or more second terminals for use with another data communication method by a variable length frame including logic channel information are accommodated by way of respective subscriber lines, comprising, the exchange having a resource divided into a first terminal resource and a second terminal resource completely separate from each other, first terminal resource control means for controlling the first terminal resource and second terminal resource control means for controlling the second terminal resource, the first terminal resource controller including fixed length cell call acceptance determinator means for determining whether or not a fixed length cell call from one of the first terminals should be accepted when the first terminal tries to use the first terminal resource, the second terminal resource control means including frame call acceptance determinator for determining whether or not a frame call from one of the second terminals should be accepted when the second terminal tries to use the second terminal resource.
The frame call acceptance determination means may includes virtual band calculator for multiplying a use requested band requested to set from one of the second terminals by a predetermined multiplexing rate to calculate a use virtual band which is controlled by the network, subscriber line free band detector for detecting a free band for the subscriber lines for the second terminal, outgoing line free band detector for detecting a free band for the outgoing lines for the second terminal, first comparator for comparing the use requested band calculated by the virtual band calculation means and the free band detected by the subscriber line free band detector with each other, second comparator for comparing the use requested band calculated by the virtual band calculator and the free band detected by the outgoing line free band detector with each other, and call acceptor for accepting a frame call from one of the second terminals when the comparison by the first comparator proves that the use virtual band is smaller than the free band of the subscriber lines for the second terminals and the comparison by the second comparator proves that the use virtual band is smaller than the free band for the outgoing lines for the second terminal.
A use requested band requested to set from one of the second terminals may be added as band information to a frame call from the second terminal and is transmitted to the virtual band calculator of the frame call acceptance determinator together with the frame call.
The frame call acceptance determination means may include virtual band setting element for setting, when setting of a frame call is requested from one of the second terminals, a physical maximum speed of the second terminal as a use virtual band for the frame call, band assurance determinator for determining whether or not a band has been assured already for a same sending subscriber as the second terminal, free band means for detecting a free band for the lines for the second terminal, comparator for comparing the use virtual band set by the virtual band setting element and the free band detected by the free band detector with each other, and call acceptor for accepting, when the band assurance determinator means determines that a band has been assured already for the same sending subscriber as the second terminal, the frame call from the second terminal unconditionally and for assuring, when the band assurance determinator determines that no band has been assured as yet for the same sending subscriber as the second terminal and the comparison by the comparator proves that the use virtual band is smaller than the free band for the lines for the second terminal, the use virtual band and accepting the frame call from the second terminal.
According to a yet further aspect of the present invention, there is provided a call acceptance determination system for a fixed length cell handling exchange in which one or more first terminals for use with a data communication method by fixed length cells each including a logic channel information section and a data section and one or more second terminals for use with another data communication method by a variable length frame including logic channel information are accommodated by way of respective subscriber lines, comprising, the exchange having a resource shared commonly by the first terminals and the second terminals, first terminal subscriber resource control means for controlling a first terminal subscriber access resource for a case wherein a fixed length cell call from one of the first terminals is inputted to the exchange by way of a corresponding one of the subscriber lines and then sent out to another one of the first terminals by way of another one of the subscriber lines, second terminal subscriber resource controller for controlling a second terminal subscriber access resource for a case wherein a frame call from one of the second terminals is inputted to the exchange by way of one of the subscriber lines and then sent out to another one of the second terminals by way of another one of the subscriber lines, and network resource controller for controlling a network common resource for a case wherein a fixed length cell call from one of the first terminals or a frame call from one of the second terminals is inputted to the exchange by way of a corresponding one of the subscriber lines and then sent out to a trunk line, the first terminal subscriber resource controller including fixed length cell call acceptance determinator for determining whether or not a fixed length cell call from one of the first terminals should be accepted when the first terminal tries to use the first terminal subscriber access resource, the second terminal resource controller including frame call acceptance determinator for determining whether or not a frame call from one of the second terminals should be accepted when the second terminal tries to use the second terminal subscriber access resource, the network resource controller including common resource call acceptance determinator means for determining whether or not a fixed length cell call from one of the first terminals or a frame call from one of the second terminals should be accepted when the first terminal or the second terminal tries to use the network common resource.
The frame call acceptance determinator may include virtual band calculator for multiplying a use requested band requested to set from one of the second terminals by a predetermined multiplexing rate to calculate a use virtual band which is controlled by the network, incoming side subscriber line free band detector for detecting a free band for the incoming side subscriber lines for the second terminal, outgoing side subscriber line free band detector for detecting a free band for the outgoing side subscriber lines for the second terminal, first comparator for comparing the use virtual band calculated by the virtual band calculator and the free band detected by the incoming side subscriber line free band detector with each other, second comparator for comparing the use virtual band calculated by the virtual band calculator and the free band detected by the outgoing side subscriber line free band detector with each other, and call acceptor for accepting a frame call from one of the second terminals when the comparison by the first comparator proves that the use virtual band is smaller than the free band for the incoming side subscriber lines for the second terminal and the comparison by the second comparator proves that the use virtual band is smaller than the free band for the outgoing side subscriber lines for the second terminal.
A use requested band requested to set from one of the second terminals may be added as band information to a frame call from the second terminal and then transferred to the virtual band calculator of the frame call acceptance determinator together with the frame call.
The common resource call acceptance determinator may include virtual band calculator for multiplying a use requested band requested to set from one of the first terminals or from one of the second terminals by a predetermined multiplexing rate to calculate a use virtual band which is controlled by the network, common resource free band detector for detecting a free band on the network common resource of the exchange, comparator for comparing the use virtual band calculated by the virtual band calculator and the free band detected by the common resource free band detector with each other, and call acceptor for accepting a fixed length cell call from one of the first terminals or a frame call from one of the second terminals when the comparison by the comparator proves that the use virtual band is smaller than the free band on the network common resource.
The predetermined multiplexing rate by which a use requested band is multiplied by the virtual band calculator may have two values set in advance including a first multiplexing rate for a use requested band requested to set from one of the first terminals and a second multiplexing rate for another use requested band requested to set from one of the second terminals.
A use requested band requested to set from one of the second terminals may be added as band information to a frame call from the second terminal and then transferred to the virtual calculator of the common resource call acceptance determinator means together with the frame call.
The common resource call acceptance determinator may include common resource fixed length cell call acceptance determinator for determining whether or not a fixed length cell call from one of the first terminals should be accepted when the first terminal tries to use the network common resource, and common resource frame call acceptance determinator for determining whether or not a frame call from one of the second terminals should be accepted when the second terminal tries to use the network common resource.
The common resource frame call acceptance determination means may include virtual band setting element for setting, when setting of a frame call is requested from one of the second terminals, a physical maximum speed of the second terminal as a use virtual band for the frame call, band assurance determinator for determining whether or not a band has been assured already for a same sending subscriber as the second terminal on the network common resource, common resource free band detector for detecting a free band on the network common resource of the exchange, comparator for comparing the use virtual band set by the virtual band setting element and the free band accepting, when the band assurance determinator determines that a band has been assured already for the same sending subscriber as the second terminal, the frame call from the second terminal unconditionally and for assuring, when the band assurance determinator determines that no band has been assured as yet for the same sending subscriber as the second terminal and the comparison by the comparator proves that the use virtual band is smaller than the free band on the network common resource, the use virtual band and accepting the frame call from the second terminal.
Alternatively, the common resource frame call acceptance determinator means may include virtual band setting means for setting a use requested band requested to set for a frame call from one of the second terminals as a use virtual band for the frame call, band assurance determinator for determining whether or not a band has been assured already for a same sending subscriber as the second terminal on the network common resource, common resource free band detector for detecting a free band on the network common resource of the exchange, first comparator for comparing, when the band assurance determinator determines that no band has been assured as yet for the same sending subscriber as the second terminal, the use virtual band set by the virtual band setting element and the free band detected by the common resource free band detector with each other, assured band extractor for extracting, when the band assurance determinator determines that a band has been assured for the same sending subscriber as the second terminal, the band assured already for the second terminal, second comparator for comparing the band extracted by the assured band extractor and a physical maximum speed of the second terminal with each other, third comparator for comparing, when the comparison by the second comparator proves that the band extracted by the assured band extractor is equal to or lower than the physical maximum speed of the second terminal, a sum of the band extracted by the assured band extractor and the use virtual band set by the virtual band setting element and the physical maximum speed of the second terminal with each other, remaining available band calculator for subtracting, when the by the third comparison comparator proves that the sum is higher than the physical maximum speed of the second terminal, the band extracted by the assured band extractor from the physical maximum speed of the second terminal to calculate a remaining available band, fourth comparator for comparing the remaining available band calculated by the remaining available band calculator and the free band detected by the common resource free band detector with each other, fifth comparator for comparing, when the by the third comparison comparator proves that the sum is equal to or lower than the physical maximum speed of the second terminal, the use virtual band set by the virtual band setting element and the free band detected by the common resource free band detector with each other, and call acceptance means for assuring, when the comparison by the first comparator or the fifth comparator proves that the use virtual band is smaller than the free band on the common resource, the use virtual band and accepting the frame call from the second terminal, for assuring, when the by the fourth comparison comparator proves that the remaining available band is smaller than the free band on the common resource, the remaining available band and accepting the frame call from the second terminal, and for accepting, when the comparison by the second comparator proves that the band extracted by the assured band extractor is higher than the physical maximum speed of the second terminal, the frame call from the second terminal unconditionally.
The call acceptance determination system may be constructed such that, for each of the second terminals connected to the exchange by way of the respective subscriber lines, a use band table is provided for controlling and storing a physical maximum speed of the second terminal and a sum total of use requested bands which have been requested to set before the present point of time by the second terminal, and the assured band extractor extracts the sum total of the use requested bands of the use band table as a band assured already for the second terminal whereas the physical maximum speed of the second terminal which is to be used by the second comparator, the third comparator and the remaining available band calculator is read out from the use band table.
A use requested band requested to set from one of the second terminals may be added as band information to a frame call from the second terminal and then transferred to the virtual band setting element of the common resource frame call acceptance determinator together with the frame call.
With the variable length frame exchanging method by a fixed length cell handling exchange and the variable length frame exchanging interface apparatus of the present invention described above, the following effects and/or advantages can be achieved.
1. A frame having a variable data length can be exchanged at a high speed by the fixed length cell handling exchange.
2. Since a predetermined corresponding relationship is provided between a used channel number upon communication of a variable length frame and data link connection identifier information and communication channel identifier information of a destination of transmission, a hard logic routing function can be provided, and when it is tried to accommodate a variable length frame terminal into the fixed length cell handling exchange, assembly and/or disassembly of a cell or routing on hardware for a variable length frame can be realized readily.
3. Since a cell relay between different fixed length cell handling exchanges is the same as in ordinary fixed length cell handling exchange, there is no need of particularly getting aware of a variable length frame, and a variable length frame terminal can be accommodated into a fixed length cell handling exchange using an existing technique as it is. Further, a service of accommodating and connecting a variable length frame terminal into and to a fixed length cell handling exchange can be realized as one of services of the fixed length cell handling exchange.
Further, with the call acceptance determination system for a fixed length cell handling exchange of the present invention, the following effects and/or advantages can be achieved.
4. By dividing the resource of a fixed length cell handling exchange simply, control of the first terminal resource and call acceptance determination can be processed completely independently of control of the second terminal resource and call acceptance determination, and a first terminal and a second terminal can be accommodated very readily into the same exchange and a service of accommodating and connecting a second terminal into and to the fixed length cell handling exchange can be realized as one of services of the fixed length cell handling exchange.
5. Since control of the first terminal subscriber access resource and call acceptance determination and control of the second terminal subscriber access resource and call acceptance determination are performed by the fixed length cell call acceptance determination means and the frame call acceptance determination means, respectively, and control of the network common resource and call acceptance determination are performed by the common resource call acceptance determination means, even where the resource of the fixed length cell handling exchange is shared commonly for the first terminals and the second terminals, a first terminal and a second terminal can be accommodated very readily into the same ATM exchange, and a service of accommodating and connecting a second terminal into and to the fixed length cell handling exchange can be realized as one of services of the fixed length cell handling exchange.
6. Since a use requested band is added as band information to a fixed length cell call or a frame call, a user of a second terminal need not any more report a use requested band every time before a call is developed, and further enhancement in service can be achieved.
7. Since at least one path from a certain second terminal is set on the lines, a band for a physical maximum speed is assured whereas a band higher than the physical maximum speed is not assured, and consequently, a contract for a speed higher than the physical maximum speed can be allowed for each of the second terminals. Then, when a second terminal is accommodated into the fixed length cell handling exchange so as to offer a service, a path for the variable length frame can be set to the fixed length cell handling switched network in the same conditions as the existing services and besides effective utilization of the resource can be realized.
8. Since call acceptance determination processing is performed using the first and second multiplexing rates conforming to characteristics of a fixed length cell call and a frame call and the common resource call acceptance determination means is divided into the common resource fixed length cell call acceptance determination means and the common resource frame call acceptance determination means, call acceptance determination processing can be performed in accordance with separate algorithms for a fixed length cell call from a first terminal and a frame call from a second terminal on the network common resource, and by assuring a band for paths for all of the second terminals as a virtual band, effective utilization of the common resource can be realized.
9. By performing call acceptance determination processing such that, when the sum total of use requested bands requested to set from a second terminal before the present point of time is lower than the physical maximum speed, a band is assured with the sum total of use requested bands, but when the sum total of use requested bands exceeds the physical maximum speed, a band is assured with the physical maximum speed, the common resource of the fixed length cell handling exchange can be utilized further effectively.
10. Since the physical maximum speed and the sum total of use requested bands requested to set before the present point of time are controlled and stored by means of the use band table for each second terminal, the sum total of use requested bands of the use band table can be used as an assured band of the second terminal, and besides, the physical maximum speed of the second terminal which is required for various comparison processing or for calculation processing of a remaining available band can be read out from the use band table and used for such processing. Consequently, control of various data and calculation processing of various means can be performed efficiently.
Further objects, features and advantages of the present invention will become apparent from the following detailed description when read in conjunction, with the accompanying drawings in which like parts or elements are denoted by like reference characters.